A wide variety of battery types are known, and among the known types, there is a class of batteries which remains inactive until a liquid has been introduced into the battery to provide a transfer path for exchanging ions between the battery electrodes; i.e., to function as an electrolyte. Most of the prior art batteries of this class are so called "one-shot" type in which a battery is actuated (for example, by dunking it into sea water) in response to an emergency situation requiring the generation of electricity. Such batteries may be found, again by way of example, as an adjunct to emergency radio beacon systems, emergency lights in marine environments, and similar applications. Such liquid activated batteries are particularly characterized by their relatively high current output and, most distinctly, their limited life which is generally measured in hours or even minutes.
A second type of liquid activated battery, which has in the past generally been deemed as little more than a laboratory curiosity, is a classical Voltaic battery in which two electrodes of differing (usually metal) materials (e.g., copper and zinc) are physically separated a short distance with a path for the communication of ions between the two electrodes being established by the provision of a liquid electrolyte. The production of a voltage difference, measurable between the two electrodes, is a consequence of the atomic and molecular structure of the chosen electrodes, and any current drawn from such batteries is accompanied by the deterioration of at least one electrode material such that the electrode material in the battery is eventually consumed. In a sense, the previously mentioned high current, short life, liquid activated batteries are simple extensions in scale of the laboratory battery with appropriate selection of electrodes and physical configurations to accommodate the desired application. But the much smaller scale batteries of this type, in simple configurations, have been thought to have little practical use until recently.
In recent years, there has been a substantial increase in the consumer use of portable electronic devices. Electronic wrist watches and pocket calculators, for example, have become commonplace. Miniaturization of components, reduction of electrical current demands, and drastically reduced costs, resulting from the advance of technology, as well as the manifest marketability of these devices, have been primarily responsible for the proliferation of these devices which are also remarkably reliable and have an extended service life, typically of many years.
Technology in the field of batteries for energizing such devices, however, has not kept pace. A typical electronic watch utilizes a battery of relatively small dimensions, on the order of 6.0 mm diameter and 2.0 mm thickness and having a voltage rating of approximately 1.5 volts d-c. Since such batteries are generally of the dry cell type they are not effectively rechargeable; the battery is, in effect, charged during the manufacturing process. As a result, deterioration of the charge begins immediately such that there is a distinct and notorious shelf life associated with such batteries.
Batteries of this type typically employ two electrodes of different metallurgical composition disposed in a spaced-apart relationship where the space between the electrodes is filled by a porous substance. At the time of manufacture, the porous substance is saturated with a liquid electrolyte which provides the ion transport medium between the two electrodes. In use or even while in storage, the saturated porous substance slowly "dries out"; and the efficiency of the ion transport by the electrolyte is reduced. When the efficiency of the electrolyte is sufficiently reduced, the electrical output of the battery drops to a level such that the battery is pronounced "dead." Since batteries of this type are of sealed-case construction to minimize the rate of evaporation of the electrolyte, it is not possible to revive the battery by adding or replenishing the electrolyte without damaging or destroying the sealed battery case. Substantial technology exists in the area of providing an effective seal for such batteries with the primary objective being the reduction of the rate of evaporation of the contained electrolyte when, in fact, the very presence of the effective seal works to prevent the rejuvenation of a depleted battery such as might be accomplished by introducing fresh electrolyte and flushing away the products of discharge and corrosion.
The batteries of this prior art type are also a source of aggravation and inconvenience for the consumer. Generally, even for a fully energized battery operating under light use, the maximum service life is generally in the range of 1-2 years. Further, the effective life in operation of these batteries can be substantially abbreviated under varying conditions of application such as in a frequently used calculator, an electronic wrist watch incorporating an audible alarm function, or an electronic wrist watch with an illumination source for the display area. Accordingly, periodic replacement, involving both time and expense as well as inconvenience to the device user, is absolutely necessary. In addition, an electronic device is rendered inoperative until replacement of an exhausted battery is accomplished which, in some situations, can be a genuinely serious drawback. For example, the failure of a calculator in use by a student during an examination is certainly serious to that student. For those with urgent need for the replacement battery and not in proximity to a supplier, the loss of use of the device can be extended and inconvenient to the extent of being critical. Further, in another aspect, it is possible that the chemicals within the battery may escape, such as by eroding its case, and cause damage to the powered device or even to the surrounding environment.
In recognition of these well-known drawbacks and deficiencies inherent in the prior art batteries for powering devices of this general category, a liquid activated battery has been developed and is the subject of broad patent protection sought under the Patent Cooperation Treaty by an application filed Jan. 20, 1987, in the United States Receiving Office and assigned Ser. No. PCT/US87/00058, that application being entitled "Liquid Activated Battery" by Patrick Cham Wong Chau and Roger L. Hummel. That application discloses a liquid activated battery with exemplary use in an electronic wrist watch which may be energized by immersing the watch in water or virtually any other water-based liquid to establish an electrolyte in the multi-cell battery which is incorporated into the wrist watch case. The battery, disclosed in several variant configurations in the aforementioned Patent Cooperation Treaty application, has been technically and commercially successful. However, experience has demonstrated that there are nonetheless significant drawbacks and deficiencies associated with the battery disclosed in the referenced Patent Cooperation Treaty application.
More specifically, to bring the voltage output of the battery up to the more or less standard voltage range required by miniature electronic devices such as electronic watch modules and calculator modules, a multi-cell battery, typically employing three cells, is required with a consequent significant complication in the physical requirements for establishing separate electrolyte reservoirs, reliably accomplishing intercell connection of the constituent electrodes, minimizing the intercell electrolytic actions, and accommodating other design and manufacturing considerations, all of which must be achieved in a small physical space.
There was a need in the battery disclosed in the referenced Patent Cooperation Treaty application to establish a relatively elaborate electrolyte filtering system. The system required the provision of a first filter for trapping particulate matter which might otherwise eventually form an internal short circuit within a cell or, if allowed to accumulate in sufficient volume, might clog up the works and inhibit the introduction of additional electrolyte. This filter stage took the form of a suitable absorptive cellular material, such as a synthetic sponge, which also served to hold the electrolyte. The sponges extended between the cell electrodes and essentially completely filled the cell chamber. A second, and decidedly important, filter stage included means for scavening dissolved oxygen, contaminants, and other gases from the liquid electrolyte which might be introduced into the battery to activate it. This second filter element, which could include materials such as silica gel and sintered ferrites, was preferably in the form of carbon granules which characteristically have a very high exposed area-tovolume ratio and very actively absorb such dissolved gases and organic contaminants. Those skilled in the art will appreciate that if the gases, particularly oxygen, can be separated from the electrolyte, the formation of corrosion (which is typically an oxide or hydroxide of the electrode material) at the electrode surfaces can be significantly inhibited resulting in a very much longer period in which rated electric current can be delivered by a cell.
Still another drawback to certain embodiments of the battery disclosed in the aforementioned Patent Cooperation Treaty application is the unintentional and undesirable creation of one or more secondary cells within a primary cell occasioned by the attachment of either or both of the two metal electrodes to the metallic conductors (wires, for example) used to transfer the generated electricity out of the electrolyte-filled cell area and onward to the connected load or into an adjacent "dry" compartment containing the power consuming device which might be, for example, an electronic watch module. This secondary cell phenomenon is caused when a metal conductor, such as ordinary tin-plated copper wire, is attached to (or even placed inclose proximity with) onemetal electrode within the electrolyte-filled (wet) compartment. The tin-plated copper wire and the electrode (presumedly of metallurgical composition different from that of the wire) form an unwanted secondary cell in the presence of the electrolyte. In yet another and more specific aspect, a tin-plated copper wire might be attached to a pure zinc electrode by means of tin-lead solder. Given the presence of copper (in the wire) and zinc (in the electrode) and tin and lead (in the solder) all immersed in a common electrolyte, there is provided the opportunity to create multiple secondary cells such that the output voltage of the primary cell becomes virtually unpredictable and therefore of little commercial value. The need for all of this coupling and connecting is, of course, occasioned by the requirement to connect multiple cells together in series to produce the desired output voltage and to connect one cell or a group of series-connected cells to an external load or power consuming device such as the electronic wrist watch module.
Another drawback to certain embodiments of the battery disclosed in the referenced Patent Cooperation Treaty application is the requirement for sponges or liquid-pervious materials placed within the electrolyte chambers and in direct contact with the metal electrodes. One skilled in the art of Corrosion Engineering quickly recognizes that undesirable corrosion of the metal electrodes will be accelerated by restricting the free circulation of the electrolyte (usually water) around the electrodes. To minimize the rate of electrode corrosion, it is also known that there should be a means for flushing away the products of incipient corrosion where such products are typically oxides and hydroxides of the metal used to form the electrode. Thus, while the synthetic sponge material disclosed in the referenced Patent Cooperation Treaty application operated to prevent the entry of particulate matter and other insoluble contaminants, the sponge material also operated to increase the rate of electrode corrosion and to restrict the flushing out of corrosion products from the electrolyte chamber.
A subtle drawback to the battery disclosed in the referenced Patent Cooperation Treaty application is the fact that, because of the cumulative effect of the points discussed above, it cannot, as a practical matter, be used to provide a predictable level of output voltage.
My invention is directed to the solution of all the drawbacks discussed above which are present in the prior art liquid activated batteries and which are inherent in the battery disclosed in Patent Cooperation Treaty application Ser. No. PCT/US87/00058 as noted above.